There are many medical, industrial, and research applications for neutrons and radioisotopes. Industrial applications include prompt gamma neutron activation analysis (“PGNAA”), neutron radiography and radioactive gas leak testing. Medical applications include brachytherapy, radioactive medicines, radioactive stents, boron neutron capture therapy (“BNCT”) and medical imaging.
Production of many useful radioisotopes requires a neutron source that provides a sufficiently high neutron flux (neutrons/cm2-second), measured as the number of neutrons passing through one square centimeter of a target in 1 second. Sufficient sustained neutron flux is generally provided by nuclear reactors. Nuclear reactors are expensive to build and maintain and ill-suited for urban environments clue to safety and regulator concerns. While many useful radioisotopes are produced by nuclear reactors, only a small number of sites around the world can generate medical isotopes in clinically relevant quantities, such as Molybdenum-99 (Mo-99) one of several isotopes in high demand in the medical field. Also, the decay rate of many useful radioisotopes makes remote production of the radioisotopes impossible because the rate of decay does not provide time for processing and transport.
Non-reactor neutron sources, such as isotopes that decay by ejecting a neutron are less expensive and more convenient. However, sources such as plutonium-beryllium sources and inertial electrostatic confinement fusion devices are incapable of generating the sustained high neutron fluxes required for many applications.
Commonly used medical isotopes are created in light water reactors fueled by critical amounts of fissile material such as uranium-235. Typically, target materials are irradiated within the reactor core for a period of time, then removed and transported to heavily shielded facilities for remote chemical processing. Other reactor types have been proposed for medical isotope production, such as “aqueous homogeneous” reactor designs, also known as “fluid fuel reactors” or “solution reactors.”
For example, U.S. Pat. No. 3,050,454 discloses a nuclear reactor system that flows fissile material in a stream through a reaction zone or core via a circulating flow path. U.S. Pat. No. 3,799,883 discloses a method for recovering molybdenum-99 involving irradiation of uranium material, dissolving the uranium material, precipitation of molybdenum by contact with alpha-benzoinoxime, and then contacting the solution with adsorbents. U.S. Pat. No. 3,914,373 discloses a method for isotope separation by the preferential formation of a complex of one isotope with a cyclic polyether and subsequent separation of the cyclic polyether containing the complexed isotope from the feed solution.
U.S. Pat. No. 4,158,700 discloses a purification method for producing technetium-99m in a dry, particulate form by eluting an adsorbant chromatographic material containing molybdenum-99 and technetium-99m with a neutral solvent system comprising an organic solvent containing from about 0.1 to less than about 10% water or from about 1 to less than about 70% of a solvent selected from the group consisting of aliphatic alcohols having 1-6 carbon atoms and separating the solvent system from the eluate whereby a dry, particulate residue is obtained containing technetium-99m, the residue being substantially free of molybdenum-99. U.S. Pat. No. 5,596,611 discloses a method of treating the fission products from a nuclear reactor through interaction with inorganic or organic chemicals to extract the medical isotopes. U.S. Pat. No. 5,596,611 attempts to provide a small nuclear reactor dedicated solely to the production of medical isotopes, where the small reactor is of a power level ranging from 100 to 300 kilowatt range, employs 20 liters of uranyl nitrate solution containing approximately 1000 grains of U-235 in a 93% enriched uranium or 100 liters of uranyl nitrate solution containing approximately 1000 grams of uranium enriched to 20% U-235. U.S. Pat. No. 5,910,971 discloses a method for the extraction of Mo-99 from uranyl sulphate nuclear fuel of a homogeneous solution reactor by means of a polymer sorbent.
Thus, nuclear reactors remain a key component in the production of useful isotopes. A key medical isotope is technitium-99m, which is a decay product of molybdenum-99. The half life of molybdenum-99 decay into technetium-99m is about 65 hours. Small lead generators are used to ship molybdenum-99 and technetium-99m to medical facilities, where the technetium-99m is added to various pharmaceutical test kits that are designed to test for a variety of illnesses. The four major suppliers of molybdenum-99 are Canada, the Netherlands, Belgium and South Africa. The United States uses about 150,000 doses per week to conduct body scans for cancer, heart disease and bone or kidney illnesses and cardiac stress tests.
Because reactors capable of producing technetium-99m (by producing molybdenum-99) only operate in a few countries, production of the important medical isotope depends both upon the export of Uranium and the reliable operation of reactors in other countries. Security and supply concerns are raised by the manufacture, export, and import process.
Nuclear reactor facilities have aged and can't be expected to continue reliable production, nor have new facilities been constructed. As an example, a 2007 month long shut down of Canada's NRU reactor in 2007 caused a worldwide shortage of technetium-99m/molybdenum 99). The Netherlands reactor for production of technetium-99m/molybdenum 99 experienced a long shut down in 2008. Other reactor shut downs have occurred in recent years in France. South Africa and other countries. Great benefit can be realized by eliminating the need for a nuclear reactor in the production of radioisotopes, which are typically produced in nuclear reactors because they generate the necessary sustained levels of high neutron flux. Operating reactors have aged, and new reactors have not been built. Many countries, including the United States, lack any facility for the production of medically important isotopes.